A 9000-year carbon isotopic record of acid-soluble organic matter in a stalagmite from Heshang Cave, central China: Paleoclimate implications

Organic matter preserved in speleothems has the potential to reflect the changes of the overlying vegetation and soil ecosystem. Here we report the first near 50-yr-resolution acid-soluble organic matter (ASOM) carbon isotope (δ13CASOM) sequence derived from a laminated stalagmite (HS-4) spanning the last 9 ky in Heshang Cave, central China. The δ13CASOM values vary between − 25.8‰ and − 22.0‰, with lower values from 9 to 4 ka BP and less negative values from 4 to 0 ka BP. We postulate that the δ13CASOM sequence is mainly controlled by temperature and water balance. Temperature could affect both vegetation physiology and microbial degradation in soil horizons. The influence of temperature on the δ13CASOM is supported by the negative correlation (r = − 0.48, p < 0.001) between the δ13CASOM record and the paleotemperature record in the nearby Dajiuhu peatland. The water balance can affect the retention time of organic matter in soils. Under drier conditions, the soil organic matter will be retained longer and is more likely to be biologically degraded, resulting in more negative δ13CASOM values. Our results reveal that δ13CASOM in speleothems has the potential to reflect the response of vegetation and/or soil processes to paleoclimate changes.